This invention relates generally to telescopic lifting jacks and more particularly to two-stage telescopic transmission jacks.
Most automotive transmission jacks used in under hoist applications are designed with telescopic rams. Telescopic rams are desirable because the transmission on the jack will be positioned at an almost work table height when the rams are not extended. Telescopic rams enable the jack to have a work table height and then extend to a maximum height of seventy-two plus inches. The maximum work height (seventy-two plus inches) provides enough clearance under the vehicle as it is suspended by an in-ground or above-ground lift for a mechanic to stand erect and make under car repairs.
Telescopic transmission jacks are designed with different types of pumps. The more expensive pumps provide faster and easier raising of the telescopic rams. The least expensive pump is designed with a single pump piston, which is activated either manually or by foot. Other pumps are activated the same way but are linked with dual pump pistons for faster rising of the rams. More expensive pumps are designed with an air activated primary ram that locks into position at its maximum height so the secondary hydraulic pump piston can be manually activated the rest of the way. Although the more expensive pumps are fast rising, there are some drawbacks to their designs. A ram activated by compressed air must have two valves. One valve controls the lifting of the primary ram with the load and one valve controls the lowering of the primary ram with the load. The primary ram can bounce or shoot up under load, if the valves are not adjusted properly, or the air cylinder is not properly lubricated. Since transmissions vary in size and weight, it is difficult to keep one valve adjustment that will satisfy all conditions. This type of pump is used with much success by mechanics who are familiar with the idiosyncrasies of the design. Other mechanics feel unsure and lack confidence in the operation of the jack.
The foregoing illustrates limitations known to exist in present two-stage transmission lifting jacks. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.